Tidal gullies in youngest peat layer of Groningen

PROCEEDINGS

OF THE

THIRD INTERNATIONAL CONGRESS

';. .i. L

OF

SEDIMENTOLOGY

,,. GRONINGEN - WAGENINGEN NETHERLANDS 5-12 JULY 1951 THE HAGUE MARTINUS NIJHOFF 1951

TIDAL ~ULLIES IN

YOUN.GEST

PEAT

LAYER OF GRONINGEN

BY

.J. VAN VEEN

THE HAGUE

1. FIVELOO AND HUNSINOO. OORINGS

During the last stages of the war 5588 borings were made in the province of Groningen, the results of which are given here. More borings have been made, as our aim was to know the exact situation of the coastal tidal gullies in the peat layer and often borings at about 5 m distance were necessary to see where the crooked gullies went. Not all those, however, could be noted down.

The results of similar investigations for Zeeland (VLAM,

1942), Westland (VLAM, 1945) and IJsselmonde (VAN VEEN, 1945)

have been published. For some other districts (Voorne, Hoekse Waard, Friesland) the invest1gations have not yet been published. The work in Groningen was begun by M. VAN DER SCHEE. Later,

E. STAMHUIS,

a bachelor of the Technical Highschool, checked the work ~f the former, found some new small gullies which had been overlooked and extended the work in general~ He also made the

ho-rings in. the cross section of the old canal which I had called .,Delf" (VAN VEEN, 1930).

Where the top layer of clayey substance was thin and the underlying peat layer thick, the shrinkage of the latter had been such that the clay-filled gullies appeared as ridges of about

½

to l m high in the field. Farmers sometimes call these ridges ,,natural dykes". In some places they have dug up parts of these ancient depots of good clay and distributed the fertile substance on their fenlands. This was the case south of the Damsterdiep. In Walcheren practically all villages, main roads and farms have been built upon these ridges. In ~roningen north of the Damster.: diep, where the clay layer is thicker, the ridges are not so well developed, and the villages and farmsteads have little relation to the old peat-time gullies.

In the· Fenlands of Cambridgeshire the same •• inversion III _of the peat soil took place. The ridges are called . ., roddons" there.

The gullies in Groningen (FIG. l) have been silted up long before 400

B.C.,

the date when the first ,,wierden" (terpen) are said to have been built up. The base of these artificial mounds 1s about 2 m above the top of the peat layer. The lapse of time

needed to deposit this silt layer of about 2 m thickness is un-known,

Inversion seems to have been of no importance at this time, as the sites of the mounds were chosen practically regardless of the silted-up gullies. Apparently the mounds were built in an un-dyked silt-region which we call ,,kwelder"-landscape (marsh). Se',;. veral mounds have been constructed on shore ridges, built up by waves in this landscape.

An island covered with shrubs or reeds may have existed du-ring the firs.t stage of mound building south of Baflo. The clayey peat substance is found there on a higher level than the peat in Fivelgo (North of Appingedam) and seems to correspond with the ,, roodoorn" type of soil in F'ivelgo. Roodoorn means ,,red veins''. The veins indicate former reed roots and the like. The name Baf-ld, which means "baften, or behind the wood" (VAN VEEN, 1951), may indicate that this wilderness already existed when the first settlers came here some centuries before the beginning of our era. The horseshoe row of mounds West, North and East of this ,, island" is very striking, Towards the South lay a low area of sticky clay, which was uninhabitable or nearly so until about

800, when it was reclaimed, The conclusion must be that, when the ,, wold", or wilderness, could exist in the last centuries B.C. of .. , Baflo at a place which is now about l m below the H. W. -level,

this sea-level must have changed considerably in relation to the land surface, because no shrub or reed can grow at a lower level than about l m above H.W.

It would Le worth while to know what vegetation covered the area of clayey peat south of Baflo, and at what height. Reed can endure brackish water of 2/3 fresh and J/3 sea water.

The wide Fivel-estuary between the wierde-row Westerwijt-werd - UskWesterwijt-werd on the western shore and the Fi velgo group in the east is quite distinct as no peat occurs here. Zeerijp (Sea-Shore) lay at the eastern shore some time after the top layers of

the. wierden were put on, e.g. 800, because this village has no wierde. Westeremden was situated at the mouth of the Fivel like (Easter) Emden at the mouth of the Ems (Emden o;: Ee-mouth = river

mouth).

The shore of the Ems, called Bocht van Watum, shows many signs of erosion. The gullies in the peat are widening towards the North and West, but not towards the East. From this i t may be inferred that in the peat-time the Ems estuary was rather far East of [lelfzijl. A few small and winding channels in the peat layer connect the Fi vel- and Ems-estuaries, but they are not im-portant. The erosion of the Bocht van Watum may have taken place essentially after the formation of the Dollard 04th century),

r o f a b o u t 2 m t h i c k n e s s i s u n -1 o f no i m p o r t a n c e a t t h i s t i m e , fiosen p r a c t i c a l l y r e g a r d l e s s o f t h e mounds were b u i l t i n an u n t w e l d e r ' l a n d s c a p e ( m a r s h ) . S e -ri on s h o r e r i d g e s , b u i l t up b y s o r r e e d s may have e x i s t e d d u -d i n g s o u t h o f B a f l o . The c l a y e y » h i g h e r l e v e l t h a n t h e p e a t i n 1 seems t o c o r r e s p o n d w i t h t h e D . Roodoorn means „ r e d v e i n s " .

Its and t h e l i k e . H i e name B a f

-nd t h e w o o d " (VAN VEEN, 1 9 5 1 ) , a l r e a d y e x i s t e d when t h e f i r s t s b e f o r e t h e b e g i n n i n g o f o u r W e s t , N o r t h a n d E a s t o f t h i s s t h e S o u t h l a y a l o w a r e a o f i b l e o r n e a r l y s o u n t i l a b o u t i c l u s i o n must be t h a t , when t h e i n t h e l a s t c e n t u r i e s B . C . o f ) u t 1 m b e l o w t h e H . W . - l e v e l , o n s i d e r a b l y i n r e l a t i o n t o t h e r e e d can g r o w a t a l o w e r l e v e l low w h a t v e g e t a t i o n c o v e r e d t h e , and a t w h a t h e i g h t . Reed can

and ] / 3 sea w a t e r , en t h e w i e r d e r o w W e s t e r w i j t -3 and t h e F i v e l g o g r o u p i n t h e t o c c u r s h e r e . Z e e r i j p ( S e a -e t i m -e a f t -e r t h -e t o p l a y -e r s o f , b e c a u s e t h i s v i l l a g e h a s no t t h e m o u t h o f t h e F i v e l l i k e Ems (Emden ^ E e - m o u t h = r i v e r

1 B o c h t v a n Watum, shows many ;he p e a t a r e w i d e n i n g t o w a r d s

t h e E a s t , From t h i s i t may be e Ems e s t u a r y was r a t h e r f a r w i n d i n g c h a n n e l s i n t h e p e a t t u a r i e s , b u t t h e y a r e n o t i m -an Watum may have t a k e n p l a c e : t h e B o l l a r d ( 1 4 t h c e n t u r y ) .

E X A M P L E OF D R I L L I N G P A T T E R N

• P E A T

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N.A.P. Hn- 2m-3m· 4m·

sm·-SOUNDING PRESSURE IN kg/cm

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NAP. Im- 2m- 3m- 4m-sm· CROSS SECTION D FIG.3

because this. wide new basin now had to be filled and emptied twice daily by the tide. No historical data, however, are avail-able about any recent erosion between Delfzijl and Watum. It is hydrologically obvious, however, that the Ems estuary must have become wider and deeper from about 1300 to 1500, when the tidal Ems basin grew to several times its origin~l size. Probably the eastern shore has been eroded more than the western. This also appears from old maps (FlG. 4.).

The general features of the buried peat landscape in Fivel-go are identical: with those found in Walcheren, Zuid Beveland and other areas near the sea. The peat layer near the sea is divided into several small islands. The areas farther inland show more peat and no more peat-islands, hut winding,. roddons" ending in the midst of wide peat-areas; cf. the Westland (VLAM, 1945), and the area ~outh of the Eemskanaal in Groningen (FIG. 1). The Dol-lard peat has been covered in yet another way (cf. chapter 3), because it was affected by a sudden burst of the dykes, a catas-trophe which occurred after the dyked peat land had shrunk al-ready.

2• THE DELF.

Ole of the instructions .to the drilling parties has been to establish cross sections of the old canal Del£, between Winsum and Delfzijl. The existence of a connection. either a river or a canal, betwe~n the Hunze and the Ems was supposed, because there were, what farmers called ,.bottomless" ditches N~ of the Delweg, and even ,,uterdieken", i.e. lands outside the dykes. Therefore there must have been (small) dykes along this waterway, which I had called .,Del£0

• The first who made a sketch of this supposed ancient, hut partly silted up canal or river, was H.P. S1EENHUIS, a teacher at Appingedam, about a century ago. Later P~M.

Bos,

a farmer at Zijldijk (Gr.) mentioned it again and called it a .,con-necting river". I was asked in 1927 by the .widow of Mr •. Bos, to write a note to Bos' map and I called the,.connecting river" a ,,canal~• named Delf" (VAN VEEN, 1930). It could now he determined by means of horings whether this canal.had existed or not, and how wide it had been. STAMHUIS made the cross-sectional horings and also two cross-sectional .,soundings" with the Barendse pres-sure-sounder. The fillings of the old canal proved to he soft and blackish fine silt. The same silt fills the meanders of the Fi-vel, which ea~ still be s~en in the fields as low pastures be-tween Westeremden and Muda. The Barendse sounder gives the force per square centimetre of an iron cone pressed into the soil. It is a well known soil-mechanical instrument used for measuring the

bearing power of the soil up to great depths. FIG. 2 gives an example of the cross-sectional borings, FIG. 3 of the .,sound-ings". Both prove that Lhe width of the canal near Westeremden was about 40 m, and the depth about 4 m below the surface.

These dimensions are quite large for a canal of an ancient date, but supposedly the tide scoured the originally narrow ca-nal, and is also responsible for the sinusoid trend, which is ap-parent over the whole length between the Hunze and the Ems, being 32 km,

I

do not think that the Del£ has been formed as a river, because in Groningen the natural rivers run in a northerly direc-tion and the general trend of the Del£ is straight and it has an east-westerly direction.

As only 8 km has been silted up and 24 km are still serving as a canal up to this present day, cross sections have been taken also in the sides of the existing canals, called Winsummer Diep and Deelster Maar in the West and Damsterdiep in the eastern part. Especially in the inner bends of the sine-curves the black-ish silt could be retraced (VAN VEEN, 1951).

Abbot Emo, the founder of Wittewierum monastry (on the ri-ver Fivel) wrote in his well known diary in 1248 that the water between Fivel and Delfzijl was called ,.Del£", and that the water of the rivulet Fivel had been diverted a long time beforell24R ,, into this Del£ to run into the Ems. The name Delfzijl is evident: sluice in the Del£. According to Emo it must have been built in 1192. There is no evidence of any earlier sluice in the Nether-lands.

A charter of 1252 calls the water between Winsum and Zout-kamp, now the Hunze-outfall, also Del£. This was one of my rea-sons to contend that a waterway had existed between the Lauwers-zee and the Ems, called Del£. The original outfall of the Hunze was North of Eenrum, through a water now called Kronme Raken. The existing Hunze-outfall might be natural and its name Del£ might be borrowed from the stretches further to the East.

Along the southern bank of the Del£ runs the ,.Delweg", the only east-west road possible in old days, lying on the narrow strip of silt land between the Fivel estuary and the lowlands. These lowlands or ,.wolds" became not cultivated before the Middle Ages, and did not provide a good foundation for any road. A local expression used in the province of Groningen is: ,.as old as Del-weg"(TER LAAN), this road apparently being considered as the sum• mum of ancientness. The name may have been originally Delfw~g; ,the stress is on the second syllable, so that the f would easily

be obliterated.

I presume that the Del£ between the Lauwers and the F.ms, was part of the much greater waterway stretching from the Middel-262

zee (Leeuwarden) via Dokkum and Ezum (Ezonstad, a place shallowed up by the Lauwerssea many centuries ago), Winsum, Appingedam, De+fzijl, .Emden to the ancient centre of the Frisians: the Up-stal•tree near Aurich in East Friesland where the annual ., thing" was held at Whitsuntide. This would be part of the still greater ,. Inner Dunes Route", which began at the Zwin in Flanders (Bruges) and in the Scheldt (Antwerp). This Del£ was made before shipping locks could be made, presumably during or immediately after the end of the invasions of the Northmen., i. e. about the year 1000. On the eastern side of the Ems at Emden we also find a canal called ,.Del f''.

L_ __ _

FlG. 4: Extract of Cortelius map of 1584.

Though waterways were priinary as to the trafic in the low 263

parts of the Netherlands, there must have been a few land roads also, like the above mentioned Delfweg. One of the old legends near Appingedam (Opwierde) is that there has been an ancient road, going in east-westerly direction, called ,.Konrebbersweg", and people say this means·,.King Redbads Way".*) Now, on Corte-lius' map,(to which my attention was drawn by Ir. T. EDELMAN) printed in 1584 (FIG. 4), we find a road going in an east-wester-ly direction passing near the places Opwierde, Delfzijl and Em-den, called ,.Robertis Regis Via". Possibly this was the main road of the Frisians leading to the Upstal-tree near Aurich.

There must have been a ferry across the Ems at Delfzijl to ,, the best of all Seven Sealands, Emsgo" (Emo). The Delfweg will have been part of this highway, as there can hardly be found an-other one going in a west-easterly direction. North of Emden to-wards Knock (East Friesland) there is a straight road, called Konrebbersweg on the modern official maps, and also on the 1945 war maps of the United States this road is mentioned by thatt name.

The water- and landroads of Redbad, or who ever it may have been, could not function for a long time. The geography of the long but narrow Frisian ,.Sealands" was such that a canal without locks and a road without paving could no't provide for the much "'needed connection. The Frisian coastal zone was split-up too much and no lasting unity could be accomplished. The main roads of the country got a N-S instead of an E-W direction. In the region of the Zuiderzee and further southward, silting was less detrimental and the., Inner Dunes Route" remained open until this day.

3. THE DOLLARD

FIG. 4 gives an extract of Cortelius' Chart (1584), indi-cating the burst of the Ems dyke opposite Emden, and the situa-tion, as Ortelius thought it was in 1277. Not before two centu-ries afterwards, the Dollard obtained its greatest extension, as the struggle for keeping the land was kept up energetically. The date 1277 is probably wrong. There was a large inundation in 1287, however, but the main date of the loss of the country may be even later. The dates of the dykes given in FIG. 5 show when the succ~eding new endykements have been made. The first dyke was

*) Redbad died in 719, but since immemorial times this popular heathen hero is considered to be the champion of the unity of the .,Seven Frisian Sealands". The oldest Frisian laws (12th century)

written by monks, who had not much liking for him, call him ,.Red• bate tha unfreth monne", Redoad Unpeaceful.

built in 1545. The greatest extension was over an area of 38.000 hectares.

We might suppose that the original fen landscape would have been totally destroyed by the sea. The horings proved, however, that the peat layer in the Dollard estuary has not entirely been . destroyed, but that it has been covered by a layer of silt. No peatless gullies are found like in the Fivelgo peat layer. There may have been ., floating islands" of peat, as Pliny reports some-where, but the main body of peat remained on the bottom and be-came covered with silt scoured in the outfall of the Ems. When dykes broke which sheltered a fen country already shrunken, a sudden covering with silt occurred.

The total amount of silt on top of the peat in the Dollard is now about 492.000.000 cub. metres. This is earth-dry silt, and if the original landscape was a fen district, as is highly pro= bable because catastrophes like this only occur where peat-land has shrunken sufficiently, the average amount of silting may be evaluated to be approximately 1 or 2 millions of cub. metres per year; that is about 2 or 3 millions about 1500, hut in our days no more than perhaps one 'half to one million". Of course, these are very rough figures.

These catastrophes produce bottle-shaped tidal basins. The neck of the bottle is situated in the silt-zone, the wide body in the peat-zone behind the silt area. Bottle shaped basins have been formed in 1421 in the Biesbos (South of Dordrecht), in the Zuiderzee (about 1300), in the lauwerszee (early), in the Dollard (about 1400) and in the Jade (Germany, about 1500). They have been disappearing slowly, except in the Zuiderzee, where silting was not of great influence.

REFERtNCES

LAAN, K. TER: Groninger Woordenboek.

VEEN,

J.

VAN, 1930: De Fivel en hare verzanding door P.M.

Bos.

Tijdschr. Kon. Ned. Aardr. Gen.

- - - , 1945: Toelichting tot de Geomorphologische kaart

van IJsselmonde. Gedenkhoek Tesch, Verh. Geol. Mijnbouwk. Gen.

• 1951: De Del£. Tijdschr. Kon. Ned. Aardr. Gen. VLAM, A.W., 1942: Historisch•morphologisch onderzoek van enige

Zeeuwse eilanden. Thesis.

- - - • 1945: Geulenkaart van het Westland. Gedenkboek Tesch, Verh. Geol. Mijnbouwk. Gen.

VRIES, W. DE, 1946: Groninger Plaatsnamen.